1. Field of the Invention
The present invention is directed to an LED (light emitting diode) array and lens array optic that creates a highly uniform illumination pattern.
2. Discussion of the Background
Due to mediocre light output, LED use in the past was primarily limited to applications where only small surface areas were illuminated. In these applications the light was concentrated into a narrow beam using an optic designed to take the wide angle light output of an LED and collimate it using a lens, discussed below with respect to FIG. 3. For high-power LEDs the collimation was accomplished using a secondary optic. Due to cost reductions and performance improvements LEDs can now be used in general illumination where large surface areas are illuminated. Examples of these applications include parking garages, parking lots, and roadways. These new applications require different optical designs. In particular these applications require high spreading of the light compared to the high collimation required for previous applications.
As per IESNA specification RP-20-98, and with reference to FIG. 4, the “basic” recommended maintained illuminance values for parking garage lighting fixtures 40 are spaced such that throughout the garage there is uniform illuminance with a maximum to minimum illuminance ratio not greater than 10 to 1, with a minimum requirement of 1 footcandle (fc) everywhere on a target area 42. In addition, a minimum vertical illuminance of 0.5 fc is required 5 feet above ground on a vertical detector 45 oriented in the vertical direction. Thus, each light fixture 40 has to illuminate an area within which the above photometric requirements are met.